JOHN GILL: Least wanted

Zebra mussels, chronic wasting disease threaten Texas wildlife

AP Photo/Texas Parks & Wildlife Department, Larry D. Hodge Non-native zebra mussels, seen attached to the interior and exterior of a pipe, are causing big headaches as they migrate into Texas waters.

SAN ANGELO, Texas - For a comprehensive look at deer breeder rules and regulations, go to www.texasparksandwildlifedepartment/deer breeder rules.

Not everything that finds its way to Texas ends up on the state's most endeared list.

The hardy mesquite tree that invaded the Southwest and Texas over 300 years ago remains today a thorn in the sides of landowners.

Mesquite came from the south with cattle belonging to Spanish explorers. Figuratively speaking, two more ill winds are blowing into Texas, but the problems this time are coming from the north.

The spread of zebra mussels and chronic wasting disease into Texas has guardians of the state's natural resources on alert.

The zebra mussel originated in the Great Lakes, and CWD, before being found in Texas, had been reported in Ohio, New Mexico and Colorado.

Zebra mussels are harmful to lakes and rivers and the game fish that live in them.

CWD has the potential of causing serious damage to the Texas deer population and, consequently, to the state's hunting industry, valued at $4.6 billion in a 2007 study.

Zebra mussels already may have established firm footing in Texas.

They first appeared in Lake Texoma. Since then, zebras have been found in Lavon, Ray Roberts and Lewisville lakes and most recently in Lake Bridgeport near Fort Worth.

Fishermen and boaters often visit several lakes in a matter of weeks, and zebra mussels can attach themselves to the bottoms of boats and trailers, invading other water bodies by hitching a ride on watercraft.

Christopher Churchill, a biologist with the U.S. Geological Survey, found the mussels in Lewisville Lake.

"This infestation is likely the result of contaminated boats being transported to Lewisville Lake, but also could be the results of downstream transportation through water flowing from Ray Roberts into the Trinity River," Churchill said.

The infested lakes form a northward-spread fan over the Dallas/Fort Worth area covering a swath of 200 miles. The Trinity flows to the Gulf of Mexico, blazing a trail through the heart of Texas along which the unwelcome mollusks might be spreading.

Zebra mussels pose negative economic and recreational effects for Texas. They attach to anything in the water, like bottoms of boats, boat motors or docks and clog municipal water plants. They have an impact on baitfish, such as competing with shad for available forage. Less forage fish results in direct hits on striped bass and catfish numbers and size.

Containment is the only cure.

"Once they are established, there is no known way to get rid of them."

An emergency order was signed July 3 adding the West Fork of the Trinity River, including Bridgeport, Eagle Mountain and Worth lakes, to the list of water bodies under special regulations intended to help control the spread of zebra mussels. The regulations require that all water be drained from boats leaving those lakes, including bilges and live wells.

The other invader, chronic wasting disease, has been nosing its way into Texas since 2010, said Mitch Lockwood, deer program leader for the Texas Parks & Wildlife Department. It is a type of transmissible spongiform encephalopathy, and always fatal.

"CWD is a progressive disease, and once an animal comes in contact, they always die," Lockwood said. "It was first detected in Colorado in 1967 and by 1978 had spread to a dozen states and two Canadian provinces."

The plague can spread to all cervids — members of the deer family — including mule deer, white-tailed deer, elk and moose. It can be spread by contaminated deer crossing state borders into Texas — mainly from New Mexico — or by deer breeders bringing sick deer into the state.

Animals can contract CWD by eating grass from contaminated soil, and it can occur in animals born in captivity or in the wild. The TPWD has found the disease in Culberson, Brewster, Pecos and Hudspeth counties and has divided the area into three containment zones.

The most severe zone, contaminated areas, is surrounded by high-risk and buffer zones. Testing has been underway for two years, and since then eight mule deer have been confirmed to have CWD.

Deer tested are taken from selective harvests and by the sampling of roadkill animals.

During hunting season all deer harvested in the protective zones are required to pass through check stations at several points in far West Texas.

"Although a limited number of white-tailed deer reside in the same far West Texas counties, none have been found to have the disease," said Lockwood.

Controlling the spread of CWD, especially by human action, has been a goal of the TPWD for many years. There are hundreds of deer breeders in Texas, and all are supposed to adhere to strict Parks and Wildlife Department rules for transporting deer to Texas.

"We have found some breeders over the years that did not follow the rules, and as a result deer at these sites were destroyed in order to prevent possible CWD contamination of our native herds," said Steve Lightfoot, spokesman for the TPWD.